At present, vitamin E is used frequently in premature neonates to prevent hemolytic anemia of prematurity caused by a relative lack of this vitamin. Beneficial effects of vitamin E administration have been recorded in retrolental fibroplasia and bronchopulmonary dysplasia. So far, very few deleterious effects have been described after administration of vitamin E to humans. Premature infants have many maturational defects in their immune system and are susceptible to severe infections which may cause death or serious brain damage. Recently, we and others have obtained evidence that vitamin E may impair the capacity of granulocytes to kill ingested bacteria. At the same time, vitamin E may have beneficial effects by enhancing phagocytosis by granulocyte in man, and antibody formation and T cell immunity in experimental animals. Vitamin E, therefore, may have good as well as bad effects in humans. The effects of vitamin E administration on the health and immune system of prematures have, until now, not been examined. We propose to study the clinical and immunological status of premature newborns on diets with or without supplemental vitamin E, using surveillance of their health status and a number of immunological tests to establish whether presently used doses of vitamin E have beneficial, deleterious, or no discernible effects.